Low voltage means electrical voltages of up to 1000 volts AC or 1500 volts DC.
Circuit breakers monitor the current flowing through them by way of a conductor and interrupt the electric current or energy flow to an energy sink or a load, this being called tripping, when current limit values or current/time period limit values, that is to say when a current value lasts for a certain time period, are exceeded. Interruption is performed, for example, by contacts of the circuit breaker which are opened.
Within the meaning of embodiments of the invention, circuit breaker means, in particular, switches as are used in low-voltage installations for currents of from 63 to 6300 amperes. Molded case circuit breakers are especially used for currents of from 63 to 1600 amperes, in particular of from 125 to 630 or 1200 amperes. Air circuit breakers are used, in particular, for currents of from 630 to 6300 amperes, especially of from 1200 to 6300 amperes.
Air circuit breakers are termed ACB for short, and molded case circuit breakers are termed MCCB for short.
Within the meaning of embodiments of the invention, circuit breaker means, in particular, circuit breakers with an electronic trip unit, ETU for short. Energy supply of the circuit breaker means, in particular, the energy supply of the electronic trip unit.
Using current converters, a power can be magnetically output from an alternating current flowing in a primary conductor to a surrounding secondary winding. Current converters are a form of transformer. One problem with current converters is the fact that the apparent power of this current converter is determined by the current level in the primary conductor. The power which is output on the secondary side is dependent on the current in the primary conductor. If a connected load, such as an electronics system for example, e.g. an electronic trip unit of a circuit breaker, is intended to be supplied with energy, the energy requirement of the load and the minimum expected primary current are determined by the dimensioning of the current converter (magnetic material, core cross section, number of turns etc.).
A sufficient amount of energy for the load is emitted above the minimum expected primary current.
One specific property of circuit breakers is that they are intended to protect against overload and short-circuit currents in the monitored electrical circuit or supply system. Therefore, a very large primary current range has to be assumed when designing the current converter. The ratio between the expected minimum primary current and the maximum short-circuit current can be more than 1:1000.
As a result, the current converter and the connected load have to be specially dimensioned.
The use of current converters with an additional magnetic shunt, which limits the level of the secondary current and therefore the secondary power, is common. The development and the manufacture of converters of this kind require considerable expenditure in respect of time and costs. Furthermore, a current converter of this kind requires a relatively large installation space since, in addition to the magnetic main circuit, an additional second magnetic circuit in the form of a magnetic shunt has to be provided.
Since the apparent power of the current converter nevertheless increases as the primary current increases, this increase in power has to be dealt with on the load side.
To this end, the current flow in the secondary circuit was further previously interrupted by a switch. However, very high and dangerous induced voltages are dropped across the secondary winding in this case, it being possible to technically manage The voltages only with difficulty.